Tuning means for cavity resonators



Ap D. cs. CLIFFORD 2,419,121

TUNING MEANS FOR CAVITY RESONATQRS Filed Oct. 17, 1942 .34 .32 n. sou/12c:

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4 ATTORNEY Patented Apr. 15, 1947 VUNITED STATES PATENT OFFICE TUNING MEANS FOR CAVITY RESONATORS David Gordon Clifford, Montclair, N. J assignor to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania Application October 17, 1942, Serial No. 462,347

Claims.

This invention relates to tuning means, and more particularly to tuning means for a micro- Wave generator of the resonant hollow-body type.

The use of resonant cavities as an integral part of an electronic device and within the envelope or vacuum enclosure thereof, presents the problem of tuning the cavities to proper resonant frequency. According to present practice, tuning is commonly effected by obtaining a mechanical change in the dimensions of the cavity by one means or another, such as by thermal expansion of thermal responsive elements, by operator-manipulated screws, and similar devices. The basic principle of the resonator is that it is an integral part of an electron discharge device and forms therewith an oscillating circuit having such mechanical configuration as to provide an electrostatic field parallel to the electron trajectory, said electrostatic field existing between two parallel planes or other appropriate surfaces, whose physical separation is a design factor in the operation of the device, and change in the separation thereof affects the oscillating period of the device. Use of the mentioned control means for effecting the change of relation of the resonator parts incurs certain limitations of rapidity of response, or range, of scope of utility, and other limitations as well as involving various diificulties of manufacture and maintenance of evacuation.

The present invention accordingly has for its general object to overcome the prior art limitations and difliculties and produce a commercial and practical microwave generator with tuning means incorporated as part thereof.

More specifically, an object of the invention is to provide a, tuning means, operation whereof does not alter the Volume of the evacuated region within the envelope. I

Another object of the invention is to accomplish a physical movement of mechanical parts within the envelope for tuning purposes without protrusion of moving parts through or utilization of moving parts as an exterior surface portion of the envelope.

A further object of the invention is to provide a tuning means which will be prompt in its response to control and may be readily and accurately manipulated by the operator or automatically manipulated, as desired.

Yet another object'of the invention is to provide a tuning means enabling a desired sweep to be effected over a frequency range.

Still further objects of the invention will appear as the description progresses both by direct men- 2 tion thereof and by implication'from the context.

Referring to the accompanying drawing in which like numerals of reference are used in all views upon corresponding parts: T

Figure 1 is a longitudinal sectional view of a micro-wave generator incorporating, my invention therewith; and

Figures 2 and 3 are cross-sectional views on lines lI--II and III-III respectively.

In the specific embodiment of the invention illustrated in said drawing, the reference numeral l0 designates an evacuated envelope here shown as of generally cylindrical configuration and fabricated from glass asrepresentative of an appropriate dielectric. This envelope is rigid through-- out and does not have any moving parts projecting therethrough. Normal to the axis of the envelope, Within said envelope, is provided a cathode or emitting surface H adapted to be heated by a filamentary heater 12 for instigating a beam of electrons longitudinally of the envelope in what will be termed, for convenience, a forward or upward direction. In the forward path of the electrons, the same pass through two parallel gridlike structures I3, I4 transverse to said path and which form a constriction or gap i5 therebetween as part of a resonator chamber 16 of generally annular shape. Beyond the second one of the grid-like structures in the path of the electrons is positioned arefiector ll.

In the general assembly of cathode, grid structures, resonator, constriction and reflector, the construction will be recognized as a reflex type of hollow-body resonant micro-wave generator wherein the forwardly moving electrons are bunched in passing through theconstriction and give up energy when passing through in bunches on the reflected or return path. Tuning of the resonant chamber 16 is obtained by changing the spacing of the constriction 15. To make such change, the forward wall l8 of the chamber I6 is made flexible, and as the whole resonant chamber must necessarily present a conductive surface,

the flexibility is obtained by utilization of a flex ible corrugated metallic diaphragm as shown. The mid-part of said diaphragm has an appropriate aperture therethrough for passage of the electrons, and the second grid-like structure l4 covers the opening to maintain the continuity of the wall as far as possible and with as little inter-- ference as possible to the-flowof electrons therethrough. The structure thus far described constitutes an electron discharge assembly of hollow body resonant cavity type.

Controlof-positionand movement otthe dia:

I I 3 phragm l8 constitutes an essential feature of the present invention. As shown, a shell or other suitable mechanical part I9 is attached near the opening through the diaphragm to said diaphragm and extends to a position upwardly or forwardly beyond the reflector where opposite edge portions of said shell are connected by a transverse saddle 20 extending through appropriate slots 2| in the reflector mounting 22. The walls of the shell depending from the saddle 20 act as stirrups therefrom to the diaphragm and will flex the diaphragm in the direction of movement of the saddle. The saddle is carried at a mid-part thereof by a rod 23 which extends axially of and forwardly out of the reflector support which is shown hollow and open at its forward end. Said rod passes through a supporting plate 24 and bearing 25 carried thereby and projects into a diametrically reduced part or neck portion 25 of the envelope. Within said neck portion and fixed on said rod 23 is a head 21 functioning as a solenoid core and composed of suitable material of magnetic-responsive material, of which iron is an example. Preferably, however, the said head or core is of an alloy having high permeability and of lighter weight than iron, various alloys of the character being available on the market. While said head 2? is preferably very close to the inside wall of the envelope neck, it is out of contact from said wall and freely movable longitudinally of the same.

Core or head 21, rod 23, saddle 20 and shell l9 are all secured together and will be referred to as the movable unitv Said unit is actuated by an appropriate spring 23 in a direction tending to reduce the spacing or gap between the grid structures, The diaphragm resiliency opposes deflection to some extent, and the position assumed by the diaphragm-carried grid under influence of the resiliency of both the diaphragm and spring in equilibrium will be when effecting the maximum constriction of the gap between the grids. To increase the gap, the unit is moved forwardly, adverse to the resilient pressure of the spring. For moving said unit, a solenoid coil 29 is situated around the envelope neck and unit head. A direct current applied to said coil will obtain the desired movement of the head or core and corresponding movement of the diaphragm and increase in the gap l5. As the magnetic influence is proportional to the applied current, the amount of movement of the diaphragm and grid structure carried thereby is readily under control, as by a rheostat 30, and can be maintained at desired spacing thereby. Indicative of a source of direct current, a battery 3| is shown in series with the rheostat and solenoid coil.

For rapid sweepingover a frequency range of the resonator, an alternating current may also be used for operating the solenoid. Accordingly a source 32 for A. C. voltage is introduced in series with the source of D. C. potential, by means of transformer 34 permitting introduction of a frequency variation proportional to the amplitude of the A. C. voltage. The upper limit of the rate of sweep will be determined by the mechanical constants of the vibratory system, mass, elasticity and damping. The sweep will efiect a broad tuning with the mean frequency determined by the D. C. current and whenthe desired frequency is obtained by'simultaneously tuning with the D. C. tuning means, the switch 33 for the A. C. circuit may be opened and the device maintained at the desired'frequency by the continued influence of the D. C. current flowing in the solenoid coil. It may now be stated, that plate 211 is preferably of a metal having high permeability and is interposed between the solenoid and the electron discharge portion of the device so as to shield the electron stream from influence in direction or intensity by the magnetic field.

In a free moving system of the character above described, motion of the diaphragm due to vibration and jarring of the device will be dampened by the constants of the system. Such constants can be chosen to minimize adverse effects. In addition, one or more copper rings 34 may be embedded in the head or core 21 to act as electromagnetic brakes, said rings resisting any motion not due to the field of the magnet.

This effect i due to movement of the rings in the magnetic field setting up an induced current and magnetic field opposed by the field of the coil. Since the E. M. F. induced will be proportional to the rate of change displacement, the more violent the shock the greater the damping effect.

It may be further added that the present tuning means has other advantages than those expressly referred to above over previous tuning devices for hollow-body resonant generators and the like. It should be particularly noted that the solenoid coil is outside of the envelope and that there are no working parts extending through the envelope and no movable parts or diaphragms forming part of the outer surface of the envelope, so that the internal volume and pressure remain constant in the device of this invention. The fixed and rigid nature of the envelope overcomes any tendency of leaks occurring from moving parts. The rapidity of response of the system is far greater than that of other known constructions and arrangements. The impedance of the solenoid can be made to match whatever device i used to feed A. C. power for sweep purposes. The range of the device may be such as to eliminate the necessity of accurately pretuning the resonant cavity during manufacture, and the tuning range is far greater than can be accomplished by thermal means.

It should be understood that this invention is not limited to the configuration shown, but applies to any configuration of envelope and to other constructions of mechanism comprising the hollow-body resonant generator or the like and appropriate modification of the invention to accommodate it to such constructions.

I claim:

1. A hollow body resonator electron discharge device comprising an envelope having acathode therein and an opposed electrode toward which electrons travel in a beam from the cathode, a resonator having walls in said envelope transverse to the path of the electron beam, said walls having openings and grids interposed in the path of the electron beam across said resonator wall openings, one of said transverse walls and its grid being movable toward and away from the other transverse wall and its grid for varying the spacing between said grids, a saddle bridging the resonator wall openings, stirrups connecting the saddle with the movable transverse wall intermediate the outer edge and opening of said movable transverse wall, a core attached with respect to and movable with the saddle, stirrups and movable transverse wall, said core being entirely within said envelope, and a solenoid coil entirely outside said envelope and at a part thereof'around said core for moving and holding said core and, wall in moved position with all movement occurring within said envelope.

2. A hollow body resonator electron discharge device comprising an envelope having a cathode therein and an opposed electrode toward which electrons travel in a beam from the cathode, said electrode having a transverse portion and a cylindrical mounting extending from the edge of said transverse portion, said mounting having opposite longitudinal openings therein, a resonator having walls in said envelope transverse to the path of the electron beam, said walls having openings and grids interposed in the path of the electron beam across said resonator wall openings, one of said transverse walls and its grid being movable toward and away from the other transverse wall and its grid for varying the spacing between said grids, a saddle bridging the resonator wall openings and passing through said openings of the electrode mounting, stirrups connecting the outer ends of the saddle with the movable transverse wall intermediate the outer edge and openin of said movable transverse wall, a, core attached with respect to and movable with the saddle, stirrups and movable transverse wall and constituting therewith means for flexing said movable wall and holding its grid covered opening in adjusted position, said means being entirely within said envelope, and magnetic means exterior to said envelope effective within the envelope for actuating said means.

3. An electronic device comprising an envelope providing a hollow body resonator therein, said resonator having a movable wall with an opening therethrough, a grid over said opening attached to and movable with said movable wall, a cathode opposite said opening for producing a, stream of electrons therethrough, magnetic means at an end of and exterior to said envelope effective within the envelope and remote from said cathode for moving said movable wall and grid, and a shield substantially impervious to passage therethrough of magnetic flux, said shield being interposed between said magnetic means and cathode for protecting the cathode stream from influence by the magnetic field of said magnetic means.

4. An electronic device comprising an evacuated envelope providing a. hollow neck projecting coaxially to one end thereof of magnetically perme- 5o able material, a solenoid, coil exterior to and around said neck, a piston within said neck and coil and constituting a movable core for the solenoid coil and slidably guided by said envelope neck, electrodes in said envelope coaxial thereto and axially alined with said piston remote therefrom, and a rod secured with respect to one of said electrodes and to said piston for moving said one electrode by movement of the piston, said piston, rod and electrodes all being entirely within the envelope whereby all movement of piston, rod and said one electrode is confined within the envelope and completely within the vacuum in said envelope.

5. An electronic device comprising an evacuated envelope providing a hollow neck of magnetically permeable material projecting coaxially at one end thereof, a solenoid coil exterior to and around said neck, a piston of magnetically responsive material substantially of equal diameter as and of less length than the interior of said neck, said piston being slidably movable within and guided by said neck and constituting a longitudinally movable core for the solenoid coil, electrodes in said envelope coaxial thereto and axially alined with said piston remote therefrom, and a rod secured with respect to one of said electrodes and to said piston for moving said one electrode by movement of the piston, said piston, rod and electrodes all being entirely within the envelope whereby all movement of piston, rod and said one electrode is confined within the envelope and completely within the vacuum in said envelope.

DAVID GORDON CLIFFORD.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,108,640 Bieling Feb. 15, 1938 2,053,930 Winter, Jr Sept. 8, 1936 2,259,690 Hansen et a1 Oct. 21, 1941 2,242,275 Varian May 20, 1941 2,272,211 Kohler Feb. 10, 1942 2,312,919 Litton Mar. 2, 1943 FOREIGN PATENTS Number Country Date 543,400 British Feb. 24, 1942 

